This invention relates to an electronic musical instrument, and more particularly to an electronic musical instrument provided with a plurality of tone production channels less than the number of keys.
In an electronic musical instrument having the upper keyboard generally used for melody performance and the lower keyboard generally used for accompaniment performance, the tones produced by the upper keyboard and those by the lower keyboard have usually different tone colors, with the result that a plurality of the upper keyboard production channels and a plurality of the lower keyboard channels should be constructed independently of one another. One of the conventional electronic musical instruments of this type is disclosed in U.S. Pat. No. 4,192,211. The number of the production channels provided for the upper keyboard and that for the lower keyboard shall be equal the number of maximum tones to be produced simultaneously, e.g., around 10, since there are cases when performance is made by both hands using only the upper keyboard, or using only the lower keyboard. In general, however, melody performance is made by one hand (right hand) using the upper keyboard, and accompaniment performance by the other hand (left hand) using the lower keyboard. In this case, both the number of the upper keyboard production channels and the lower keyboard production channels are considerably smaller than the total number of channels by one to three channels for each keyboard, and many production channels remain unused.
On the other hand, in electronic musical instruments having only a single keyboard, it is in practice that the keyboard is divided into the higher tone key range for the melody performance and the lower tone key range for the accompaniment performance with tones of different tone colors thus being produced. In this type of electronic musical instrument, a plurality of tone production channels are provided independently of each other correspondingly to the melody and accompaniment, and usually the number of channels is not so large. This is to prevent wastefulness caused by the presence of unused production channels and to reduce the manufacturing cost. However, it involves an inconvenience that when a free performance is attempted, e.g., when multiple tones are to be performed simultaneously by the melody tone color, departing from the range of the expected mode of performance, e.g., one tone for melody and simultaneous 3 tones for accompaniment, the performance cannot be made by an electronic musical instrument having only a limited number of melody production channels.
To solve the above problem, an electronic musical instrument was proposed by the application serial No. 182,464 entitled "Electronic Musical Instrument with Plural Tone Production Channels" dated Aug. 28, 1980, (and assigned to the same assignee as the present case) in which arrangement was made that the relationship between the tone production channels and key ranges (or keyboards) would not be fixed but be made variable according to the performance mode, i.e., all production channels could be set to produce melody tones through the whole keyboard or the tone production channels could be used divided between the melody tone (specific key range tone) and accompaniment tone (different key range tone). According to the preceding application, the manufacturing cost can be reduced as a result that the total number of tone production channels can be reduced, and either a performance mode (normal mode) for melody performance only or a performance mode (automatic bass/chord mode) for both melody performance and accompaniment performance is made possible without any trouble through the effective utilization of production channels according to the performance mode, but it has a possibility of the following inconvenience occurring at the time of performance mode shift.
Though there is be no problem if the performance mode switching operation is performed providing sufficient time before starting keyboard performance, when the performance mode switching operation is performed during key depression performance or during a short period such as in the interlude, the tone assigned to a channel before changing the mode remains even after changing the mode in spite of the shift in the tone production mode made at the channel by the mode change, with the resultant possible production of unnecessary tones. For example, assume that the production channels are A, B, C, D and E, all 5 channels A to E are used for melody tones in the normal mode, channels A and B are used for melody tones and channels C, D and E are used for accompaniment tones in the automatic bass/chord mode, and the mode change has taken place from the normal mode to the automatic bass/chord mode while a melody tone assigned to any of the channels C, D and E is being produced. In this case, the channels C, D and E are changed to the channels for accompaniment tones after the mode shift. However, since melody tone assignment before the mode change remains, the tones depressed for the melody performance are produced from the channels C, D and E for the accompaniment tones. Conversely, when the mode is changed from the automatic bass/chord mode to the normal mode while an accompaniment tone assigned to any of the channels C, D and E is being produced, the same inconvenience as above occurs. In addition, since the performance mode change time is a transitional period during which the tone production manner of each tone production channel in the tone production assignment circuit or the tone production circuit is changed, unexpected inconvenience in the tone production assignment of the tone, if any, may occur. Furthermore, when the mode is changed from the normal mode wherein all tone production channels are used for melody tones to the automatic bass/chord mode wherein the tone production channels are used divided between melody tones and accompaniment tones, if the depression of the keys corresponding to the melody tones assigned to the tone production channels changed to be used for accompaniment tones is continued, the melody tone is reassigned to any of the tone production channels for the new melody because that melody tone is not assigned to new melody tone production channel as already mentioned. At this time, if a percussive group envelope tone color, e.g., piano, has been selected as a melody tone, the percussive tone is produced twice as if key depression were made twice, even when key depression is actually continued. The first tone production is when the key is actually depressed (all tone production channels are used for melody tones), and the second tone production is executed immediately after reassignment from the channel changed to accompaniment tone production channel by the performance mode switching operation to melody tone production channel. The detail is illustrated by way of a simple example, as follows.
It is assumed that the are tone production channels A, B, C, D and E and that channels A and B are used for melody tones and channels C, D and E are used for accompaniment tones when the tone production channels are divided. When a certain key of the melody key range (or keyboard) is depressed in the normal mode in which all channels A through E are used for melody tones and the assignment is made to channel C, a percussive type envelope signal is formed in channel C synchronously with the signal (key-on signal) indicating key depression, and the melody tone with percussive type envelope is produced. When the performance mode is shifted to the automatic bass/chord mode while the depression of the key corresponding to the melody tone assigned to said channel C is continued, the melody tone assignment at said channel C is released since channel C turns out to be for an accompaniment tone. However, since the depression of the key corresponding to the melody tone so far assigned to channel C is continued, processing is made to reassign the tone to either channel A or B for melody in the automatic bass/chord mode. Reassignment is required to assure the continuous tone production when tone color of tone with continuous type envelope is selected as a melody tone color instead of percussive group. However, this reassignment causes trouble when tone color of tone with percussive type envelope is selected as melody tone color. For example, if reassignment is made to channel A, a signal (key-on signal) indicating key depression rises at channel A, and a percussive type envelope signal is formed corresponding to said channel A synchronously with said signal rise. Accordingly, the melody tone with percussive type envelope is produced correspondingly to the actual key depression at channel C before the performance mode switching operation and the same percussive melody tone as at channel C is produced again at channel A corresponding to the reassignment immediately after the performance mode switching operation in spite of the fact that the key is kept depressed thereafter.